The present invention relates to a zigzag pattern changing device for use in a sewing machine and, in particular, to such sewing machine zigzag pattern changing device which is suitable for forming different needle swing patterns easily.
Conventionally, in a sewing machine which is capable of forming a needle swing pattern such as a zigzag or other similar patterns, there is disposed a needle swing device which, in a sewing operation, moves a vertically moving needle in a horizontal direction intersecting at right angles to a cloth feeding direction to thereby be able to control a needle drop position.
The conventional needle swing device includes a needle swing cam connected to the main shaft of the sewing machine in such a manner that it is rotated once each time the sewing machine main shaft is rotated a given number of times; and, in the needle swing cam, there is formed a cam groove which controls the needle drop position each time the sewing machine main shaft is rotated once to form a given needle swing pattern. In particular, a needle bar is swung right and left along the cam shape of the cam groove to thereby control the needle drop position.
Now, in FIGS. 29 and 30, there is shown the conventional needle swing device. In FIG. 29, a pulley 10 is fixed to the rear end of an upper shaft (main shaft) 2 supported rotatably on the machine frame of a sewing machine main body 1, and the pulley 10 is connected to a sewing machine motor (not shown) through a belt (not shown) wound around the pulley 10. In the interior portion of the machine frame of the sewing machine main body 1, a well-known needle bar drive mechanism (not shown) comprising a crank and the like is provided between the upper shaft 2 and a needle bar 3 in such a manner that the needle bar 3 can be moved up and down once each time the upper shaft 2 is rotated once. The needle bar 3 is supported in a vertically movable manner by a needle swing arm 4 which is formed in a substantially U-like shape.
A cam drive shaft 11 which has a horizontally extending axis crossing at right angles to the axial direction of the upper shaft 2 is rotatably supported by a frame of the sewing machine body 1; and, on the rear end side of the cam drive shaft 11 protruding into a space portion 1A formed on the rear side of the sewing machine body 1 (on right hand of FIG. 30), there is fixed a needle swing cam 13 including a sewing machine main body front side surface thereof (on left side of FIG. 30) a cam groove 12 which is formed on the circumference thereof and is shiftable in position in the diameter direction thereof to control the needle swing motion, while a cover 14 is removably mounted on the sewing machine main body 1 in such a manner that it covers the space portion 1A. Also, on the front end side of the cam drive shaft 11, there is fixed a cam drive gear 15. In operation, the cam drive shaft 11 can be driven or rotated deceleratingly through a worm wheel 17 rotatable in linking with a lower shaft (not shown) connected to the upper shaft 2 as mentioned above, a transmission gear 16 fixed on the same shaft as the worm wheel 17, and the cam drive gear 15 meshingly engageable with the transmission gear 16.
As shown in FIG. 30, a needle swing drive shaft 20, which is arranged in parallel to the cam drive shaft 11, is rotatably supported on the sewing machine main body machine frame. And, to the rear end side of the needle swing drive shaft 20 which protrudes into the space portion 1A, there is fixed the base end of a cam arm which supports on the leading end thereof a cam roller 19 engageable with the cam groove 12, while the base end portion of a needle swing drive arm 21 is fixed to the middle portion of the needle swing drive shaft 20. Also, as shown in FIG. 29, the lower end portion of a drive rod 22 is rotatably supported on the leading end portion of the needle swing drive arm 21 by a pin 23.
In FIG. 29, a needle swing shaft 5, which supports the needle swing arm 4 on one end thereof in a fixed manner, is supported movably in the axial direction (in FIG. 29, in the right and left direction) thereof by a bearing portion 6 which is formed in the machine frame of the sewing machine main body 1. Also, to the other end of the needle swing shaft 5, there is connected one end (in FIG. 29, the left end) of a needle swing drive link 7 through a joint 8 such that it is rotatable around a horizontal axis. And, the other end (in FIG. 29, the right end) of the needle swing drive link 7 is rotatably connected to the leading end of a swing width change link 9, while the upper end of the drive rod 22 is connected to the middle portion of the needle swing drive link 7.
The base end of the swing width change link 9, by operating an operation lever (not shown) from outside the machine frame of the sewing machine main body 1, can be shifted or moved in the vertical direction and can be secured to the vertically shifted position; that is, the needle swing width can be changed by means of such secured position.
In the above-structured conventional sewing machine needle swing device, if the lower shaft is rotated in linking with the rotational driving of the upper shaft 2, then the worm wheel 17 is rotationally driven in linking with the lower shaft, the rotational force of the worm wheel 17 is transmitted through the transmission gear 16 to the cam drive gear 15 to thereby rotate the cam drive shaft 11, so that the needle swing cam 13 is rotated. And, the cam groove 12 is then radially displaced due to the rotation of the needle swing cam 13 and the cam roller 19 follows the rotational motion of the cam groove 12, thereby causing the cam arm 18 to swing. The swinging motion of the cam arm 18 then swings the needle swing drive arm 21 formed integrally with the needle swing drive shaft 20, so that the drive rod 22 can be reciprocated in the vertical direction.
When the vertical motion of the drive rod 22 is transmitted to the needle swing drive link 7, then the needle swing drive link 7 is swung, while the swinging motion thereof is restricted by the swinging motion of the swing width change link 9 about the base end (in FIG. 29, the left end) thereof. Therefore, the needle swing drive link 7 is swung in the horizontal direction due to the horizontal-direction component of the swinging motion of the swing width change link 9. As a result of this, the needle swing shaft 5 is swung in the axial direction thereof through the joint 8 and thus the needle swing arm 4 is swung in the horizontal direction to thereby to cause the needle bar 3 supported thereon to carry out its needle swing operation, so that a needle swing pattern can be, formed.
By the way, in the conventional sewing machine needle swing device, when forming, as a needle swing pattern, different needle swing patterns, for example, a two-dot zigzag shown in FIG. 31 and a four-dot zigzag shown in FIG. 32, such pattern formation is executed by replacing the needle swing cam 13.
Therefore, when changing the needle swing pattern, after the cam cover 14 is removed to thereby remove nuts or the like, the needle swing cam 13 is removed and replaced with a new needle swing cam 13 in which a cam groove 12 having a desired shape is formed. This replacement operation requires much labor, time and skill in dismantling and assembling associated parts.
In view of this, for example, as disclosed in Unexamined Japanese Patent Application Publication No. Hei. 8-117463, there is conventionally proposed a sewing machine needle swing pattern changing device which is able to form different needle swing patterns easily without replacing the needle swing cam 13 with a new one.
Here, in FIG. 33, there is shown an embodiment of a sewing machine needle swing pattern changing device which is disclosed in Unexamined Japanese Patent Application Publication No. Hei. 8-117463. In this device, on the inner wall of a sewing machine main body 1, there is journaled a cam drive shaft 11 which extends in the longitudinal direction of the sewing machine main body 1 and can be rotationally driven by means of the rotation of a lower shaft (not shown) through a drive transmission mechanism; and, on the rear end portion of the cam drive shaft 11, there is mounted by a screw 24 a needle swing cam 13 which includes cam grooves 12a and 12b formed on the two surface sides thereof and having their respective desired shapes. The two cam grooves 12a and 12b are respectively so formed as to have their own desired needle patterns which are frequently selected: for example, one cam groove 12a is so formed to have a cam shape capable of forming such a two-point zigzag as shown in FIG. 31, whereas the other cam groove 12b is so formed to have a cam shape capable of forming such a four-point zigzag as shown in FIG. 32; that is, the two cam grooves are respectively have two kinds of cam shapes which allow the formation of the needle swing patterns that are used relatively frequently.
A needle swing drive shaft 20 is rotatably journaled in parallel to the cam drive shaft 11, while a cam body 25 is loosely fitted with one end portion of the needle swing drive shaft 20. On the outer periphery of the needle swing drive shaft 20, there is formed a key groove 26 which extends in the axial direction thereof. A key 27, which is referred to as a sliding key, is mounted in the key groove 26. In the inner periphery of the cam body 25, there is formed a key groove 28 which can be slidably fitted with the key 27. And, due to the rotational motion of the cam body 25, the needle swing drive shaft 20 can be rotated integrally with the cam body 25.
Also, in the two end portions of the cam body 25, there are two cam arms 18a and 18b which are formed integrally with their respective cam body end portions and also which are projected on the two sides of the cam body 25 with the needle swing cam 13 between them. In the respective leading end portions of the two cam arms 18a and 18b, there are mounted support shafts 30 which project in the mutually opposing directions. Also, on the respective support shafts 30, there are mounted cam rollers 19a and 19b which can be respectively engaged with the cam grooves 12a and 12b. These cam rollers 19a and 19b are structured such that, when one cam roller 19a is in engagement with the cam groove 12a on one surface side, the other cam roller 19b is prevented from being engaged with the cam groove 12b on the other surface side.
Also, on one end face of the cam body 25, there is provided a screw shaft 31 having a male screw formed on the outer periphery thereof; and, the screw shaft 31 is formed integrally with the cam body 25 end face and is also structured such that it is coaxial with the needle swing drive shaft 20. Further, the screw shaft 31 is rotatably supported by a support plate 32 which is mounted on the inner wall of the sewing machine main body 1. With the outer peripheral side of the screw shaft 31, there is threadedly engaged a rotary bush 34 serving as a moving mechanism 33 which extends through the support plate 32 from the inside thereof and also which, when changing the needle swing pattern, moves the cam body 25 in the axial direction thereof; and, to the portion of the rotary bush 34 located on the outside portion of the support plate 32, there is fixed a switching dial 35. This switching dial 35 prevents the rotary bush 34 from moving in the axial direction with respect to the support plate 32. Also, with the leading end portion of the screw shaft 31, there is threadedly engaged a lock nut 36. Further, on the support plate 32, there is mounted a cam cover 14 which is used to cover the needle swing cam 13. The remaining portions of the present device are similar in structure to the previously described conventional sewing machine needle swing device and thus the description thereof is omitted here.
In the thus structured sewing machine needle swing device, when changing the needle swing operation, with the lock nut 36 loosened, the switching dial 35 is rotationally operated to thereby rotate the rotary bush 34 serving as the moving mechanism 33. In this case since the rotary bush 34 is supported by the support plate 32 and is thus prevented from moving in the axial direction, only the screw shaft 31 is moved in the axial direction, so that the cam body 25 is moved along the needle swing drive shaft 20. And, the engagement of the cam roller 19a, which has been engaged with one cam groove 12b of the needle swing cam 13, is removed, whereas the other cam roller 19a is brought into engagement with the cam groove 12b.
After then, if the needle swing cam 13 is driven or rotated, then the needle bar can be driven by the cam shape of the cam groove 12b, that is, by a different needle swing operation from that of the cam groove 12a, thereby being able to form a different needle swing pattern.
In other words, the rotational operation of the switching dial 35 allows easy switching of the needle swing patterns.
By the way, as the conventional sewing machine zigzag pattern changing device, there is also proposed a device which, instead of the needle swing cam 13 with the cam grooves 12a and 12b formed therein, employs a needle swing cam comprising a conjugate cam (not shown) which includes different cam surfaces on the outer peripheral surfaces thereof.
However, in the conventional sewing machine zigzag pattern changing device disclosed in the above patent publication and shown in FIG. 33, there are raised various problems which result from the needle swing pattern changing structure thereof.
For example, when changing the needle swing pattern, the key groove 28 formed in the inner periphery of the cam body 25 is slid along the axially-extending key 27 mounted in the key groove 26 formed in the outer periphery of the needle swing drive shaft 20. In this structure, however, the cam body 25 cannot be moved smoothly in the axial direction of the needle swing drive shaft 20 due to the sliding resistance thereof.
Also, because the working and assembling precision of these key grooves 26, 28 and key 27 requires a high degree of technical skill, the manufacturing costs thereof are expensive. At the same time, when an error or the like is produced while they are being worked and assembled together, the cam body 25 and needle swing drive shaft 20 are made loose with respect to each other in the rotation direction of the needle swing drive shaft 20, and this loose condition or play is amplified before it is transmitted to the needle bar 3, that is, the needle bar 3 is made loose on both right and left side thereof (a so-called needle bar right and left play), so that a given needle swing position cannot be set, which results in the lowered sewing quality.
Further, the occurrence of such loose condition between the cam body 25 and needle swing drive shaft 20 applies an excessive overload, in more particular, a shearing load due to a shock to the key 27 each time the needle swing cam 13 is driven or rotated and the swinging motion of the cam arm 18 of the cam body 25 is thereby transmitted to the needle swing drive shaft 20, that is, each time a sewing operation is executed, so that the key 27 can be broken.
Also, in the mechanism shown in FIG. 33, when the cam body 25 is moved along the needle swing drive shaft 20 in order to change the needle swing pattern, for example, one cam roller 19a in engagement with one cam groove 12a of the needle swing cam 13 is separated from the cam groove 12a, that is, the engagement between them is removed and, at the same time, the other cam roller 19b situated at a non-engaging position is made to advance into the other cam groove 12b of the needle swing cam 13 so that it is thereby engaged with the other cam groove 12b. The engagement or removal of the cam rollers 19a and 19b with or from the cam grooves 12a and 12b must be carried out at the same time and, therefore, the two cam rollers 19a and 19b are set at positions respectively opposed to the cam grooves 12a and 12b, that is, at a switch point SP which is shown in FIG. 34. For this reason, when changing the needle swing pattern, the needle swing cam 13 must be stopped in a phase which provides the switching point SP. However, since such phase is difficult to find out, there is necessary a vast amount of labor or a highly skilled technique, which leads to the lowered operation efficiency.
Also, the occurrence of such loose condition between the cam body 25 and needle swing drive shaft 20 changes the positions of the respective cam rollers 19a and 19b, thereby causing the switch point SP of the needle swing cam 13 to vary when changing the needle swing pattern, which increases the labor and time necessary for the switching operation further.
Further, when changing the needle swing pattern, as shown in FIG. 35, the cam rollers 19a and 19b can be both engaged with the cam grooves 12a and 12b in the middle of the needle swing pattern changing operation. Therefore, when the movement of the cam body 25 along the needle swing drive shaft 20 is insufficient due to a mistake made by an operator, there is a possibility that the sewing machine can be driven with the cam rollers 19a and 19b respectively in engagement with the cam grooves 12a and 12b to thereby cause the zigzag pattern changing device to be broken.
In addition, there are found similar problems even in the zigzag pattern changing device which employs a needle swing cam comprising a conjugate cam.
In view of the circumstances of the conventional zigzag pattern changing devices, there is the need for development of a sewing machine zigzag pattern changing device which is able to change the needle swing pattern easily and properly.
The present invention aims at eliminating the drawbacks found in the conventional sewing machine zigzag pattern changing devices. Accordingly, it is an object of the invention to provide a sewing machine zigzag pattern changing device which is able to change different needle swing patterns over to each other easily and properly, without replacing a needle swing cam.